Basic concepts
Respiration, or breathing, is important for homeostasis.
What is ventilation?
Ventilation is the movement of air into and out of the lungs. Ventilation is also called breathing. Breathing has two stages.
a. Breathing in or inhalation or inspiration
In this stage of breathing, air flows into the lungs.
a. Breathing out or exhalation or expiration
In this stage, the air flows out of the lungs.
What is respiration?
Respiration is the diffusion of gases across plasma membranes.
Types of respiration
There are two major types of respiration
1. Pulmonary respiration, or external respiration,
It is the exchange of gases between the atmospheric air in the lungs and the blood.
2. Systemic respiration, or internal respiration
It is the exchange of gases between the blood and the body’s cells.
Types of respiration based on the respiratory organs
The following are the common types of respiration based on respiratory structures.
Pulmonary respiration: Occurs in the lungs, involving gas exchange between alveoli and blood. (e.g., amphibians, reptiles, birds, and mammals)
Branchial respiration: Occurs in gills, involves gas exchange between water and blood (e.g., fish).
Tracheal respiration: Involves air-filled tubes (tracheae) that bring oxygen directly to cells (e.g., insects).
The respiratory system
The respiratory system consists of the structures used to exchange respiratory gases (oxygen and carbon dioxide) between air and blood.
Division of the respiratory tract
The respiratory tract is separated into two regions:
A. The upper respiratory tract
The upper respiratory tract includes the nose, pharynx, and larynx.
B. The lower respiratory tract
The lower respiratory tract includes the structures from the trachea through the alveoli in the lungs.
The upper and lower respiratory tracts can be further subdivided based on their functions.
a. The conducting zone
It encompasses the structures from the nose to the smallest air tubes within the lungs. These are used for ventilation.
b. The respiratory zone
The respiratory zone consists of small air tubes (respiratory bronchioles) and the alveoli. Gas exchange occurs within the respiratory zone.
Structures of the respiratory system
a. External nose.
The external nose encloses the nasal cavity. It is the first and only external part of the respiratory system.
b. Nasal cavity.
It is lined with the mucus membrane and cilia. It helps clean, warm, and humidify inspired air.
c. Pharynx.
The pharynx is commonly called the throat. It serves as a common passageway for food and air.
d. Larynx.
The larynx is also called the voice box. It is a rigid cartilaginous structure that helps keep the airway open. It also helps in sound production.
e. Trachea.
The trachea is commonly known as the windpipe. It serves as an air passageway and helps clean inspired air.
f. Bronchi.
The bronchi are tubes that direct air into the lungs. Bronchi divide and redevide forming fine airways called bronchioles.
g. Lungs.
Human beings have two lungs. Each lung has a network of air sacs, called alveoli, and capillaries. Each air sac is the site of gas exchange between the air and the blood.
Functions of the respiratory system
The respiratory system performs the following functions:
1. Regulation of blood pH.
The respiratory system removes CO2 from the blood and, therefore, helps in maintaining normal blood pH.
2. Production of angiotensin-converting enzyme (ACE)
The ACE helps in blood pressure regulation.
3. Voice production.
Air moving past the vocal folds produces sound and therefore makes speech possible.
4. Olfaction.
The nasal cavity has the olfactory epithelium; therefore, the sensation of smell occurs when airborne molecules are drawn into the nasal cavity
5. Protection.
The respiratory system serves as the first line of defense, providing protection against some microorganisms by preventing them from entering the blood.
Importance of the respiratory system
Breathing is necessary because all living cells of the body require oxygen and produce carbon dioxide. The respiratory system exchanges these gases between the air and the blood, and the cardiovascular system transports them between the lungs and the body cells
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